The depressor anguli oris is a triangular muscle pulling the corner of the mouth downward, the antagonist of the zygomaticus major. Its action expresses sadness and displeasure, and hyperactivity of the depressor anguli oris in ageing produces the downward corner of the mouth that characterises the marionette line deformity. Marginal mandibular branch facial nerve palsy selectively paralyses this muscle along with the depressor labii inferioris, producing a characteristic asymmetric smile pattern.
| Origin | Oblique line of the mandible |
|---|---|
| Insertion | Angle of the mouth, modiolus |
| Nerve Supply | Marginal mandibular branch of the facial nerve (CN VII) |
| Blood Supply | Facial artery |
| Actions |
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|---|
Antagonising the zygomaticus major in facial expression, the depressor anguli oris produces the downturned mouth of displeasure or sadness and contributes to the nasolabial fold morphology and lower face ageing appearance.
Botulinum toxin injection into the hyperactive depressor anguli oris is used to elevate a persistently downturned mouth corner, one of the most effective treatments for the marionette line deformity of facial ageing. Marginal mandibular nerve palsy from parotid surgery or trauma produces ipsilateral depressor anguli oris and depressor labii inferioris paralysis, creating an asymmetric smile where the lower lip on the affected side cannot be depressed during broad smiling, a subtle but distressing asymmetry.
The depressor anguli oris is palpable as a triangular muscle along the lateral chin radiating from the mandibular oblique line to the mouth corner, becoming firm during downward mouth angle depression.
Selective weakness of the lower lip depressors from marginal mandibular branch injury during parotid or submandibular surgery, producing lower lip asymmetry during broad smiling that is distressing and may require selective botulinum toxin to the contralateral normal side for symmetry restoration.
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